Recently, elements including minute structures formed by MEMS (micro electro mechanical systems) technique find wide application in various technical fields. The elements include micro movable elements including minute movable parts, such as a micro-mirror element, an angular velocity sensor, an acceleration sensor, etc. The micro-mirror element is utilized as an element which serves a light reflecting function, in the field of optical communication techniques or optical disk techniques, for example. The angular velocity sensor and the acceleration sensor are utilized for applications such as image stabilizing functions for video cameras or mobile phones with cameras, car navigation systems, airbag ignition timing system, attitude controlling systems of vehicles or robots, etc. Such micro movable elements are described in the following Patent Documents 1-4, for example.
[Patent Document 1] Japanese Laid-open Patent Publication No. 2003-19700
[Patent Document 2] Japanese Laid-open Patent Publication No. 2004-341364
[Patent Document 3] Japanese Laid-open Patent Publication No. 2005-305582
[Patent Document 4] Japanese Laid-open Patent Publication No. 2006-72252
FIGS. 39-41 depict an example of a related art micro movable element 90. FIG. 39 is a plane view of the micro movable element 90. FIGS. 40 and 41 depict sectional views along a line XL-XL and a line XLI-XLI in FIG. 39, respectively.
The micro movable element 90 includes a movable main part 91; a frame 92 surrounding the movable main part 91; a frame 93 surrounding the frame 92; a pair of torsion bars 94 coupling the movable main part 91 and the frame 92; and a pair of torsion bars 95 coupling the frame 92 and the frame 93. The pair of torsion bars 94 defines an axis B1 of rotation of the movable main part 91, and the pair of torsion bars 95 defines an axis B2 of rotation of the frame 92 and thus the movable main part 91. The axis B1 and the axis B2 intersect perpendicularly. In other words, the micro movable element 90 is a so-called oscillating element in two axes.
If the micro movable element 90 is configured as a micro-mirror element, for example, a mirror surface 91a is provided on the movable main part 91, and a predetermined first actuator (not illustrated) for generating a driving force for the rotation of the movable main part 91 around the axis B1 is provided. Further, a predetermined second actuator (not illustrated) for generating a driving force for the rotation of the frame 92 and thus the movable main part 91 around the axis B2 is provided. The movable main part 91 is driven to rotate or oscillate around the respective axes B1, B2 by operating the actuators as appropriate. Such driving oscillation of the movable main part 91 causes a reflecting direction in which an optical signal is reflected by the mirror surface 91a on the movable main part 91 be changed.
Further, if the micro movable element 90 is configured as an angular velocity sensor, opposed capacitance electrodes for detection (not illustrated) are provided as a pair on the movable main part 91 and the frame 92, respectively. The capacitance electrodes for detection have capacitances changed according to the rotation amount of the movable main part 91 around the axis B1, for example. Further, a predetermined actuator (not illustrated) for generating a driving force for the rotation of the frame 92 and thus the movable main part 91 around the axis B2 is provided. The actuator is operated to cause the frame 92 and thus the movable main part 91 to oscillate around the axis B2 at a predetermined frequency or cycle. When a predetermined angular velocity is applied to the movable main part 91 in such an oscillated state, the movable main part 91 rotates around the axis B1 and thus the capacitance between the capacitance electrodes for detection changes. The rotation amount of the movable main part 91 is detected based on the change in the capacitance, and the angular velocity applied to the movable main part 91 or the micro movable element 91 is derived based on the detection result.
According to the related art techniques, when a micro movable element array is configured by aligning plural micro movable elements 90 as described above in a row and sharing the frame 93 among the micro movable elements 90 to integrate them, it may be difficult to implement a sufficiently high population of the micro movable elements 91 in the element arranged direction. The reason is as follows.
The respective parts of the micro movable element array or the micro movable element 90 are formed from a material substrate using the MEMS technique. Thus, when an air gap is formed by penetrating the material substrate with a certain thickness, there is a limit to the minimum width of the air gap in term of processing technique. In other words, it may not be possible to reduce the spaced distances between the neighboring micro movable elements 90 of the micro movable element array below the processing limit. Therefore, it may not be possible to reduce the spaced distances between the movable main parts 91 of the neighboring micro movable elements 90 below the processing limit.
Further, the micro movable elements 90 of the micro movable element array have movable parts which are driven electrically. Thus, in the micro movable element array it is preferable to ensure the spaced distance between the neighboring micro movable elements 90 which is required to avoid mechanical interference or electric interference.
Due to the processing limit, the preference to avoid the mechanical interference, and the preference to avoid the electrical interference, as described above, according to the related art techniques, there is a case in which it is difficult to implement a sufficiently high population of the micro movable elements 91 in the element arranged direction.
If the sufficiently high population of the micro movable elements 91 in the element arranged direction cannot be implemented, there may be a case where the functionality of the micro movable element array including plural micro movable elements cannot be sufficiently enhanced. For example, a case is assumed where the micro movable elements 90 are micro-mirror elements and the micro movable element array is the micro-mirror element array installed in a wavelength-selective-optical switching device. In this case, the lower the population of the micro movable elements 91 in the element arranged direction becomes, the more the loss of the optical signals, which are received by the micro-mirror element array as a whole and reflected by the mirror surfaces, becomes. For example, a case is assumed where the micro movable elements 90 are angular velocity sensors or acceleration sensors and the micro movable element array is a sensing device. In this case, the lower the population of the micro movable elements 91 in the element arranged direction becomes, the more sensitive to noise the detection signal becomes and thus the sensitivity of the sensor is reduced. It is predicted that the plural neighboring micro movable elements 90 have a noise canceling effect between the neighboring micro movable elements 90 for the noise generated by the micro movable elements 90; however, the lower the population of the micro movable elements 91 in the element arranged direction becomes, the more the noise canceling effect or noise reduction effect is reduced.